Passive Position Sensing 1 Introduction

Figure 2: Circuit diagram of a resolver.

As discussed in class, there are 2 ways of using a resolver to make angular measurements. The first way (pictured above) is to energize the rotor winding with an AC reference signal (5 to 10 volts at a frequency of 1 KHz to 10 KHz). The AC reference signal will be coupled to the 2 stator windings, with the amplitude of each induced stator voltage being proportional to the cosine of the angle between the stator winding and the rotor winding. Because of the 90o separation between the 2 stator windings, the amplitude of the output voltage from the stator windings will be proportional to the sine and cosine of the rotor angle. Note that if the rotor angle is  , (referenced to, say, stator winding #1) then the output voltage from stator windings #1 and #2 will be respectively (equations (2.1) and (2.2))

Now if we increase  by 180 degrees, the output voltage from stator windings #1 and #2 will be

It is important to note the fact that while the amplitudes of these two signals have remained unchanged, their phases have reversed. Thus to decode a full 360o , we need some sort of phase sensitive detector, a simple rectifier will not be sufficient.

The second way to use a resolver in making angular measurements is to energize the two stator windings with two AC reference signals (5 to 10 volts at a frequency of 1 kHz to 10 kHz) bearing a 90o phase shift with each other and measure the induced voltage on the rotor winding (Figure 3).